Existing uncertainties of the etiology and treatment rationale of many oral and facial conditions associated with pain (e.g., trigeminal neuralgia, toothache and referred pain) largely are reflections of considerable gaps in our knowledge of the neural mechanisms underlying pain. Since our own research has been successful in providing some of the insight into these mechanisms related to dental and facial pain, we propose to extend our recent studies to an examination of the afferent input to the trigeminal brain stem nucleus caudalis from the tooth pulp and other orofacial tissues. With microelectrode recordings in caudalis we will characterize nociceptive and mechanoreceptive inputs to single neurones and study the regulatory effects of interacting peripheral (e.g. tooth pulp and tactile) and central (e.g. periaqueductal gray matter) stimuli, many of which produce pain or analgesia in man and animals. Possible presynaptic regulatory mechanisms underlying the effects observed in caudalis and previously noted by us in more rostral brain stem nuclei will be clarified by microelectrode recordings in the trigeminal ganglion from single identified primary afferents supplying pulp or cutaneous nociceptors an mechanoreceptors. Methods previously employed by the applicant will be utilized for this; these involve noting changes in the antidromic excitability of the brain stem endings of these identified units by peripheral and central stimulation. The method will also allow us to assess the influence of caudalis on the excitability of those afferents projecting to the more rostral nuclei, as well as providing important information on the level of termination in the brain stem of nociceptive and mechanoreceptive afferents supplying the teeth and other orofacial structures.